EFFECTS OF SIMULATED ACID PRECIPITATION A ND LIMING ON EARTHWORM FAUNA (LUMBRICIDAE, OLIGOCHAETA) AND HUMUS TYPE IN A MATURE STAND OF NORWAY SPRUCE (HOGLWALD EXPERIMENT)

The effects of simulated acid rain and liming on the earthworm fauna w ere studied in a mature spruce stand in Southern Germany On the untrea ted control plot abundance and biomass of earthworms was about 25 indi viduals and 1.9 g/m2, respectively. Two main species occur, D. octaedr a and L. rubellus, sparsely also D. rubidus. Humus form is a typical m oder with little local variation. Frequent application of acidified ir rigation water with a pH of 2.7 to 2.8 led to a significant decrease o f the earthworm populations. The species L. rubellus and D. rubidus di sappeared entirely. The role of direct and indirect negative effects o f the acidified water is discussed. The humus form did not change so f ar. Liming caused a considerable increase of the earthworm densities, especially of L. rubellus. Three ears after liming the abundance was a bout 400 to 500 individuals per m2; it decreased again to numbers betw een 200 and 250 five years after the beginning of the experiment. Besi des the general improvement in soil reaction and base characteristics a better food source seemed to play a key role. For the observed chang e in species dominance in the limed soils interspecific competition is discussed. The humus form of limed soils also changed drastically, ca used by the enormous activities of the earthworms. During the first ye ars acidic irrigation combined with liming showed higher earthworm abu ndance and activities as compared with limed and normally irrigated su bstrates. Following, the densities decreased faster again, which could be explained with an exhaustion of food sources in the organic layer.